When an article to be processed is to be coated, it is commonly subjected to surface treatment from the viewpoint of ensuring the corrosion resistance and adhesiveness of a coating film. In particular, when a metal (metal material, metal structure) is to be coated, the metal surface is subjected to chemical conversion treatment (surface treatment) for chemically forming a chemical conversion coating film.
An example of the chemical conversion treatment is chromate conversion treatment with a chromate containing composition; however, adverse effects of chromium have been noted. In recent years, treatment with zinc phosphate treatment agents (zinc phosphate treatment), which are chromium-free treatment agents (surface treatment agents, chemical conversion treatment agents) has become widespread (see, for example, Patent Document 1).
However, the zinc phosphate treatment agent is highly reactive due to the high content of metal ions and acids that it contains, hence this treatment agent offers an unfavorable impact on both the cost and the workability during drainage treatment. In addition, metal surface treatment with the zinc phosphate treatment agent involves the generation and sedimentation of water-insoluble salts. Such precipitates are generally referred to as sludge, and the removal and disposal of sludge generates an additional undesirable cost. Furthermore, the use of phosphate ions is not preferable because they may affect the environment through eutrophication, and the treatment of phosphate ion effluent requires considerable labor. Moreover, metal surface treatment with the zinc phosphate treatment agent requires surface adjustment, which can prolong the total treatment process.
In addition to the zinc phosphate treatment agent and chromate conversion treatment agent, a chemical conversion treatment agent containing a zirconium compound is known (see, for example, Patent Document 2). The chemical conversion treatment agent including a zirconium compound is a treatment agent with concentrations of metal ions and acids which are not as high, and hence its reactivity is also not as high. This offers a favorable cost advantage and improved workability during drainage treatment. Such a chemical conversion treatment agent is also superior to the above-described zinc phosphate treatment agent in regard to the inhibition of sludge generation.
However, a chemical conversion coating film formed with a treatment agent including a zirconium compound cannot be said to have good adhesiveness to a coating film obtained by cationic electro-deposition or the like. Therefore, the treatment agent, including a zirconium compound, has been combined with phosphate ions or other components in order to improve its adhesive properties and corrosion resistance. However, the combination of phosphate ions can cause the above-described eutrophication.
Further, an increase in the coating film adhesiveness by addition of a water soluble resin component has been attempted (for example, refer to Patent Document 3). In patent Document 3, a chemical conversion treatment agent which is a metal surface treatment composition including the following constitution is disclosed. Namely, this chemical conversion treatment agent is a chemical conversion treatment agent including a water soluble resin, the water soluble resin having at least the constituent units shown by the following Formulas (1), (2).

Based on this chemical conversion treatment agent, with zirconium as a film forming component of the chemical conversion film, and fluorine as an etching agent for the metal material, their respective actions can respectively improve the corrosion resistance and adhesiveness of the metal material. Further, a water soluble resin having an amino group, specifically a polyvinylamine resin and a polyallylamine resin, by acting on not only the surface of the metal material, but also on the coating film formed after the chemical conversion treatment, can improve the adhesion between the surface of the metal material and the coating film.
Patent Document 1: Japanese Unexamined Patent Application Publication No. H10-204649
Patent Document 2: Japanese Unexamined Patent Application Publication No. H7-310189
Patent Document 3: Japanese Unexamined Patent Application Publication No. 2004-218074